Containers currently being used for transport and storage of sensitive or valuable materials are vulnerable to theft or malicious tampering. Currently, small, inexpensive mechanical seals are used to detect and validate theft attempts and tampering. These small, mechanical seals are typically standard metal, plastic, and wire devices whose casing is printed with a unique serial number. A mechanical seal used in the international shipping industry is shown in FIG. 1.
In this type of seal, the metal pin 10 is inserted into the plastic casing 12 until a latch is sprung, permanently locking the metal pin inside the casing. Because the sealed container may not be opened without visibly damaging or destroying the seal, the serial numbers printed on these seals are tracked and the casing/pin enclosure is visually inspected for external evidence of tampering. Once the transport container has arrived at the shipping destination, the seal is broken in order to open the container. Upon its removal, the seal is examined carefully for signs of mechanical tampering and possible attempts at repair. However, because this type of seal is only inspected visually, the security of the containers can be easily compromised with an accurate reproduction of a seal with the original serial number stamped on its casing. Additionally, detection of seals that are broken and repaired or replaced requires close visual inspection. Human error is a significant factor during a subjective visual inspection of mechanical seals. Also, detailed forensic examination of mechanical seals for signs of tampering usually cost more than the seal itself.
Another type of inexpensive seal currently used in the transport and storage industries is mechanical wire seals 20, similar to that shown in FIG. 2. These seals are easily affixed to a container and provide a reliable seal. They, too, must be examined carefully upon removal for signs of counterfeiting, cutting and repair, stretching, and other indications of tamper. The examinations often require the use of expensive microscopy equipment and take some time. Hence, the major cost of this type of seal is borne in its examination, rather than the cost of the actual seal.
Expensive active electronic seals are used by agencies that are charged with the storage of critical materials such as nuclear and other hazardous materials. An example of this type of seal is the active fiber-optic seal 30 shown in FIG. 3. A fiber optic loop 32 is woven through hasps on the container. Each end of the fiber optic cable is attached to a protected electronic circuit 34. At either regular or random intervals, a pulse of light is sent into the cable. A detector on the other end of the cable looks for this pulse. If the pulse is detected, then the processor in the seal assumes that the fiber optic loop has stayed closed and, therefore, no tamper of the seal is evident. If the pulse is not detected, the seal processor logs the event as a potential tamper. Each event is stored within the seal by its microprocessor with a time stamp. A personal computer serial interface is used to read the event registers in the seal. This type of seal provides an extremely high degree of tamper resistance along with quick tamper determination but at a relatively high cost. However, the cost of inspecting, reading, and evaluating the seal is very low.
A need exists for a seal system that incorporates the reliability and verifiability of sophisticated electronic safeguards with extremely low purchase and inspection costs.